Is there life on other planets?

In my August column I suggested that we have robbed our children’s children of daylight, or at least of the ability to turn night into day. This month I will expound on the theme. Man has created so much Earth-bound light pollution as to deny children the magical experience of an unimpaired view of the night sky. They are unfamiliar with the splendour of the Milky Way as it projects its faint band of light across the firmament. This contrasts to my own childhood in rural Wales where houses were lit by oil lamps and there were no lights in the streets. Consequently, a good view of the Milky Way was an almost nightly experience.

The Milky Way

Sometime soon, on a cloudless and moonless night in the depths of the countryside, I hope to lead a small group of teenagers, possibly my grandchildren and their friends, to show them the Milky Way in all its glory. I will tell them that the light emitted by the galaxy is dim because the stars are too distant to be seen individually by the naked eye. I will explain that contrary to appearances, we do not see the galaxy from afar but are ourselves a part of it.

I am certainly no astronomer and was astonished to learn that our sun was just one among no less than a hundred billion stars in the Milky Way alone. Moreover, there are as many galaxies in the universe as there are stars in the Milky Way. In other words, there are in the cosmos a hundred billion squared stars, that is 1022 or ten thousand billion billion stars.

The probability of life on other planets

There are some theological problems associated with such a large number. All religions are parochial, in the sense that they only consider the relationship between a supernatural being and the inhabitants of a single planet – Earth. It is of course true that many parameters and conditions determine whether life is created and can thrive on any particular planet (see, for example, Martin Rees’s Just Six Numbers). So it is not surprising that life evolved on only one of our solar system’s nine planets. It is, though, intriguing to ask what are the chances of life having been created on other planets revolving around stars in other galaxies?

Suppose, conservatively, that every other star in the cosmos has, on average, a single planet. Even if the chances of life forming on a particular planet were one hundred thousand billion to one, there would still exist in our cosmos a billion inhabited planets, though they would not all be within the same timeframe. Even in the vastness of space we need not feel lonely.

While on my stargazing excursion I will draw attention to the Andromeda Nebula, which contains within it a pale smudge, thought to be part of the Milky Way. However, in the 1920s Edwin Hubble demonstrated it was another galaxy, located two million light years from Earth and containing about a hundred billion stars. It is one of the furthest objects which can be seen by the naked eye. Drawn by gravity, it is hurtling towards us at roughly a hundred kilometres a second. In about five billion years the Andromeda and Milky Way galaxies will collide, though this may not be too great a concern, as the collision will coincide with the natural death of our sun.